Light scattering from tissues and cells has attracted extensive research interest, especially due to the potential it offers for in-vivo diagnosis. The starting point in light-scattering-based diagnosis is that normal and diseased tissues are characterized by scattering parameters that are measurably different. Translating such methods to the clinic requires knowledge of the optical properties associated with both healthy and diseased tissues. However, the direct measurement of these scattering parameters, which may include, but are not limited to, the scattering mean free path (MFP) ls and anisotropy factor g, is extremely challenging.                In the absence of absorption, the scattering mean free path, ls, is the average distance between two adjacent scattering events or the distance over which the unscattered light decreases to 1/e of its original power. The parameter ls, provides the characteristic length scale of the scattering process.        The anisotropy factor g is the average cosine of the scattering angle, g=<cos θ>, and is used to obtain the transport mean free path, lt=ls/(1−g), which normalizes ls to larger values to account for forward-biased scattering (i.e., g>0).        The transport mean free path lt is a new quantity, which approaches ls as the individual scattering becomes isotropic (g→0). The physical meaning of lt (and its asymptotic limit, ls) is the distance after which the direction of propagation is randomized.        
The direct measurement of the foregoing scattering parameters is extremely challenging and, therefore, simulations, such as Monte Carlo, or finite-difference time-domain simulations, are often used iteratively instead.
Recently, Fourier transform light scattering (FTLS), the spatial analog of Fourier transform spectroscopy, was developed to provide angular scattering information from phase-sensitive measurements. FTLS is described in Ding et al., Fourier Transform Light Scattering of Inhomogeneous and Dynamic Structures, Phys. Rev. Lett., vol. 101, 238102 (2008), which is incorporated herein by reference. FTLS has been used to measure ls from angular scattering of tissue slices, and the anisotropy parameter g has been determined by fitting the scattering pattern with a Gegenbauer Kernel phase function, as reported by Ding, et al., Optical properties of tissues quantified by Fourier-transform light scattering, Opt. Lett., vol. 34, pp. 1372-74 (2009), hereinafter Ding (2009), incorporated herein by reference.
Measurement of scattering parameters may serve to characterize tissue, and, in particular, the presence and nature of tumorous tissue. In particular, breast cancer and prostate cancer are two of the most widespread cancers in the western world, accounting for approximately 30% of all cases. Following abnormal screening results, a biopsy is performed to establish the existence of cancer and, if present, its grade. The pathologist's assessment of the histological slices represents the definitive diagnosis procedure in cancer pathology and guides initial therapy.
It is thus of great value to place new quantitative methods at the disposal of clinicians, insofar as they provide for assessment of biopsies with enhanced objectivity. To this end, various label-free techniques have been developed based on both the inelastic (spectroscopic) and elastic (scattering) interaction between light and tissues. Thus, significant progress has been made in near-infrared spectroscopic imaging of tissues. On the other hand, light scattering methods operate on the assumption that subtle tissue morphological modifications induced by cancer onset and development are accompanied by changes in the scattering properties and, thus, offer a non-invasive window into pathology. Despite these promising efforts, light scattering-based techniques currently have limited use in the clinic. A great challenge is posed by the insufficient knowledge of the tissue optical properties. An ideal measurement will provide the tissue scattering properties over broad spatial scales, which, to our knowledge, remains to be achieved.